A Conservative politician wants cannabis decriminalised for medicinal use - so that people in serious pain do not have to buy it on the black market.

Speaking on the day cannabis was reclassified from a B class drug to a C class substance, north Wales Assembly Member Mark Isherwood said people with illnesses like multiple sclerosis should not have to break the law to get pain relief.

From Thursday, police will no longer automatically arrest those caught in possession of cannabis, and the maximum penalty for possession has been cut from five to two years in prison.

"No-one is wishing to encourage people to break the law, but the concern is that people in pain are being criminalised when they seek what, for them, is an effective form of pain control," Mr Isherwood said.

I think the difficulty with cannabis is that there is anecdotal evidence that it is helpful, but it does not suit everybody

Dr Tony Calland, BMA

Stressing the difference between medicinal and recreational use, Mr Isherwood has called for substances derived from cannabis to be available from GPs for medicinal use on a strictly-controlled basis.

He said research was being carried out with the aim of producing a spray containing the essential ingredients.

But, he added :"In the mean time, many MS patients, and people with AIDS and cancer are going on the black market."

The British Medical Association, however, has taken a more cautious position on the issue of decriminalisation.

Talking to BBC Wales on Thursday, Dr Tony Calland, chair of the BMA in Wales, said more research needed to be done.

"You would need a re-classification of the drug," he said.

"From the BMA's point of view, we are very keen to make sure that patients in pain have the very best pain relief available.

"I think the difficulty with cannabis is that there is anecdotal evidence that it is helpful, but it does not suit everybody.

"It is a powerful drug, like many others, and I think before it could be licensed for general, or even prescribed use, it would have to undergo the same kind of testing and evidence-based kind of assessment that every other drug does."